In certain applications, it is desired to provide a wall of great thickness with at least one opening surrounded by an axially projecting lip. This is, in particular, the case for the barrels of the vessels of nuclear reactors, to which a certain number of conduits must be connected. These conduits may, in fact, be connected by welding onto the end of the lips in question, which advantageously replace the fitted standby nozzles described, for example, in FR-A-2,517,575.
However, the current techniques of forming lips of the aforementioned type, which are based on the principle of punching (see, for example, FR-A-1,198,440), are not entirely satisfactory in practice. In fact, with these processes, the connecting internal radius of the lip is the greater, the greater is the extent to which it is sought to obtain a large projection of the latter.